Found footage films get a bad rap - and worse reviews. But the genre combines the vitality of punk rock with the reach of a video viral, and it has earned, if not respectability, then at least a respectful reappraisal. Some found footage (hereafter FF) films are, admittedly, unwatchable (see The Devil Inside or, better, don't). But others, such as recent West Country-set religious chiller The Borderlands, or Bobcat Goldthwait's creepy Bigfoot hunt Willow Creek (out on May 2), are closer to unmissable.

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Beyond an ominous title card, FF films require little backstory, and the genre has only a brief history of its own. An uncompromising, hand-over-the-camera-lens look at totalitarianism in Vietnam-era America, Peter Watkins' 1971 mock-doc Punishment Park is considered FF's chief forebear. Ruggiero Deodato's still-troubling Cannibal Holocaust (1979), however, is the most striking early archetype. Following a gonzo film crew into tribal Amazonia, it puts video-nasty atrocities through a film-school filter, with Robert Kerman's professor recovering the crew's "found footage" and deciding whether to make it public, or burn it. Mary Whitehouse favoured the latter.

The turn of the millennium proved the genre's Year Zero, thanks to the double whammy of The Last Broadcast (1998) and The Blair Witch Project (1999). Although neither has dated brilliantly, they set the templates: the former cold and rigorously controlled; the latter loose, jolting and raw.

Costing $35,000, and grossing $250,000,000, The Blair Witch Project was a smash-hit, and its profitability has been the genre's main legacy. FF films are so cheap to make that they allow emerging talents to get financially viable flicks into cinemas. Perhaps the best example is Chronicle director Josh Trank, whose $12 million FF superhero flick made ten times its budget. Trank is now working on The Fantastic Four reboot.

They've even crossed genres. Alone With Her (2006) is a Hand That Rocks The Cradle-type stalker thriller (starring Colin Hanks!), The Bay (2012) an eco-disaster flick, while the VHS franchise (2012-2013), though still horror, has rejuvenated the portmanteau format.

Why such a flood of FF movies? They work. The Blair Witch Project consists of three people wandering around the woods for 90 minutes. Nothing happens. It's tense as hell. The guerilla thrills of Cloverfield (2008) knocked spots off the thematically similar War of the Worlds (2005) - despite the latter being made by the biggest director and star on the planet. More modest efforts like Atrocious (2010) and Chernobyl Diaries (2012) wring plenty of mileage from their atmospheric locations: a spooky Spanish finca, and a deserted Russian disaster site, respectively.

It's not just the budgets that are economical, the storytelling's lean and efficient too. There's no exposition; everything happens live, like real life - or sport. FF films show us the world the way we see it, from the ground up, with no establishing shots or CG vistas. Some people think its say-what-you-see aesthetic degrades the language of cinema, but that language is a beautiful lie, and FF at least offers a viable alternative.

In the Spanish infection franchise REC (2007-present, although Part III dispenses with the FF format), probably the most technically accomplished FF films ever, directors Jaume BalaguerÃ³ and Paco Plaza turn the camera into a participant. Blood obscures the lens, the sound becomes subjective as it leaches out, and the spotlight and infrared functions reveal deeper truths in the darkness. REC's last line, shrieked by traumatised TV host Manuela Velasco, could almost be the genre's mantra: "We have to tape everything, for f**k's sake!"

They may not be pretty, but that doesn't mean FF films are stupid. Cannibal Holocaust and Man Bites Dog ask searching questions about our appetites for violence and voyeurism ("We might be the savages!" concludes the former). Cloverfield's 9/11-inspired NYC alien attack anticipates the blurry iPhone grabs of citizen journalism. The paranoid theories of The Conspiracy (2012) are as persuasive as any news report. And the chilling, self-shot Zero Day (2003), which shows two teens plotting a terrible Columbine-alike crime, is profound and appropriate â€“ the banality of evil captured in the most banal manner possible.

Finally, and this is the genre's get-out-of-jail-free card, FF films are frightening. When The Blair Witch Project's Heather Donohue screams, "What the f**k is that?" at nothing - literally nothing - it might be horror's most cost-effective scare. Paranormal Activity (2007) conjured chills (and four sequels, so far) from slamming doors and shifting bed sheets.

FF sequences are even starting to appear in "normal" cinema. Some of the strongest scenes in Wolf Creek, The Descent (both 2005) and Lake Mungo (2008), good candidates for the best non-FF horrors of the Noughties, play out on camcorders and video phones as the characters look on helpless.

Mostly, as REC and The Blair Witch Project prove so effectively, FF films put the focus back on faces, on fear - things that get lost in the maelstrom of SFX. After all, one of the scariest things in cinema is also the simplest: watching other people being scared.